You're talking about two different things here. How a character gains power, that's a role-playing issue. That's all fluff. Maybe my wizard learned his spells from the ghost of a red dragon, and has to sacrifice some food every morning to regain spells. Maybe they're brought every morning by imps from the elemental plane. Maybe they were tattooed on his skin by an evil slavemaster, and he spends his life trying to understand what's written on him. Maybe his "spellbook" is his hair, braided with knots and little stones that dictate each spell.
Different concepts, same mechanics, same class.
I think what you want are clearly different mechanics, but those mechanics ought to be disentangled from the fluff, and they should be clear and different. This "like better weapon proficiencies, combat capability and hit points than the wizard" just sounds like a fighter/wizard, and this "a spontanoeus caster needs at least double the number of slots/spellpoints/mana and more mundane abilites (hit points, proficiencies an even attack bonuses)" just sounds broken. You don't mention anything about restrictions, just "spontaneous caster", so presumably he gets all spells a wizard does, per day, and doubled(!), unlimited known spells, more hit points, better weapons, etc etc.
IMC, I rebuilt the sorcerer as a hybrid/gish class. Spontaneous casting, but very limited spell selection, martial weapons, etc, etc. I also use occult (pact/bargaining) magic as a third type, alongside arcane and divine (and psionic, actually. Innate magic probably constitutes a fifth type). Shamans, witches, and cultists all use occult magic.
